The present invention relates to technology of apparatuses and methods which detect color bleeding and color distortions occurring adjacent to monochrome areas of pictures read while a transfer speed of a document is fluctuating, and relates to an image reading apparatus that reads documents while moving relative to the document and reading means, particularly the present invention comprises an image sensor that has, for example, a primary color sensor line and an image reading apparatus that simultaneously reads documents in three colors to acquire image data.
As a single-package image sensor, there are so-called three-line color sensors that have three lines of sensors which are equipped with a primary color filter in the photoelectric transducers of each line. Not only can this three-line color sensor comprise an image reading apparatus (hereinafter referred to as color scanner) that reads color and be compact in size compared to using three one-line only image sensors, but also the manufacturing processing of the manufacturer is adjusted in order that the gaps between the three lines are within the design requirements. Consequently, position adjustments for users are simplified. Another advantage is the fact that it can read color documents at high speeds while sequentially lighting a primary color light source compared to the so-called light source switching method.
There are two representative types of color scanners which use this type of three-line color sensor. One of these is called a fixed document type color scanner that reads documents secured onto a glass surface while moving an optical read system, and the other one is called a sheet pass type color scanner that has a fixed optical read system and reads documents by conveying the document being conveyed by conveyance means.
Sheet pass type color scanners which feed one sheet at a time from a stack of documents and then read the documents as they move through the scanner lack stability and have fluctuations in the images due to ripples and fluttering in the conveyance process of the documents or shocks caused by documents separating from the retaining point (nip point) of the transfer roller used to convey documents. In addition, shapes containing false errors in the original picture also occur as image data.
A sheet pass type includes a sheet pass color scanner that integrates the conveyance unit into the apparatus as well as a type of scanner in which a document feeding apparatus that separates and feeds documents from a document stack one at a time (hereinafter referred to as ADF: automatic document feeder) is installed in the above-mentioned fixed document type color scanner. In order to respond to recent demands from users who want to read double-sided documents, a composition has also emerged that holds the image reading unit within the ADF and reads both sides of the document on the color scanner and the ADF.
A fixed document type color scanner that fixes and reads documents does not exhibit unstable behavior in documents and is assumed to be able to provide stable document reads. Even with fixed document types, in a color scanner with a high-resolution read, vibrations and oscillations exist in the sub-scanning direction (direction of movement) or shuddering traversing the reading direction of the optical carriage that integrates a mirror carriage and optical system to form read lines, appear in the image just like when there are ripples in a document.
When abnormal images, which are false pictures, are contained in original pictures at random locations within an image acquired in this manner (in particular, color distortions and color bleeding occurring at monochrome achromatic color areas), it is difficult to detect where these images exist, thereby increasing the desire for a definitive solution. Thereupon, an object of the present invention is to take these problems into consideration and provide an apparatus and a method that can extract characteristics from already acquired image data and detect the locations in the images where color distortions and color bleeding occur without using an especially complicated or special configuration.
The read position differs on the surface of a document in a so-called three-line simultaneous read system that uses a three-line color sensor in which photoelectric transducers within one package are arranged in three primary color lines to read documents. Because of this, when the document is not conveyed evenly, the read position on the image data will become inconsistent with the intervals in the composition of the image sensor, resulting in the occurrence of blurring in the image. The position of the read lines which read the three primary colors of the document surface can be made to coincide in order to avoid this. Japanese Patent Publication (Tokkai) No. 07-143281 (prior art-1) is an example from this point of view. In this example, a dispersion element such as a prism is placed in the optical path in an optical reduction system. This method, however, requires the dispersion position to coincide with the positions of each color line of the image sensor, thereby requiring very precise adjustments which in turn leads to considerable manufacturing processes and in particular makes the adjustment process complicated making this an undesirable method.
Japanese Patent Publication (Tokkai) No. 08-163316 (prior art-2) teaches a device wherein a document is read and the image data analyzed with black regions being detected from each color data. This is performed together with the brightness varying to a large degree, namely, the focal point targeting high contrast areas (edge regions between white and black), a determination being made as to whether or not the locations of each of the three primary colors coincide at this location and the color distortion portion being detected and corrected. In this disclosure, however, only the utilization of brightness for the method to detect black locations was disclosed while a detection method with good achromatic color accuracy is not.
Furthermore, Japanese Patent Publication (Tokkai) No. 08-139949 (prior art-3) teaches technology wherein a correlation function is used as a detection method of color saturation regions. This document also disclosed that when peak values and the total value of the correlation function are observed, it is possible to distinguish between chromatic color regions due to position read errors or fundamental low-frequency chromatic color regions (color areas) and improve the performance of read error separation from similarly shaped original images because of equivalence due to auto-correlation, for example, read errors accompanying simple shapes such as thin lines. The fact that auto-correlation determination must be introduced results in a composition that governs calculations.
The first object of the present invention is to build a color saturation means that identifies color saturation regions based on calculations which use both original image data values and negative image data values in order to obtain color saturation detection without using cross-correlation that requires an execution time. The first object of the present invention is also to provide an image determination apparatus equipped with a color bleed determination means that detects whether color bleeds are present at locations the color saturation means has identified as monochrome regions and an image reading apparatus and image determination method equipped with this image determination apparatus.
The second object of the present invention is to build a color saturation means that identifies color saturation regions from the magnitude of cumulative values after L*a*b* conversion of the three primary colors R, G and B using table conversion in order to obtain color saturation detection without using cross-correlation that requires an execution time. The second object of the present invention is also to provide an image determination apparatus equipped with a color bleed determination means that detects whether color bleeds are present at locations the color saturation means has identified as monochrome regions and an image reading apparatus and image determination method equipped with this image determination apparatus.
The third object of the present invention is to divide examined regions based on the magnitude of deviation values along with introducing distributed arithmetic for the purpose of standard deviation calculations when calculating correlations to determine whether high color saturation color bleeding is present after obtaining a division of the color/monochrome regions. The third object of the present invention is also to provide an image determination apparatus comprising a simplified error detection means and an image reading apparatus and image determination method equipped with this image determination apparatus.